Noted an error in my newly upgraded instance of Dynamics 365 and Marketo today. I was attempting to sync records into Dynamics 365 and noticed this error in the Activity Log for person records I attempted to sync:

It seems that in the upgrade to Dynamics 365 there are permissions that the Marketo Sync User needs to have that are missing. The error above relates to privileges to the entity in Dynamics called "User Entity UI Settings" that the sync user needs access to.

Here is how to edit the Security Role for the Marketo Sync User in Dynamics 365 to enable permissions to that entity:

Step 1: Navigate to Settings, Security

Step 2: Select Security Roles

Step 3: Navigate to select the Marketo Sync User Security Role (note: in your instance this may have been named something different than "Marketo Sync User")

Step 4: Navigate to find the entity called "User Entity UI Settings" on the Core Records tab and click on the label on the left to enable access to the Marketo Sync User so it matches the image below:

If you now navigate back to Marketo and attempt again to sync the record you saw the error on you should see no error. Below is a record in Marketo before, and after the above changes were done in Dynamics 365: